Crushers with ring-shaped track and roller

ABSTRACT

A grinder having an annular track with a horizontal axis (14), a roller (16) capable of travelling over the track, a mechanism for pressing the roller against the track and means (18) for displacing the material from one edge of the track to the other in such a way that it passes several times beneath the roller before being evacuated. To enhance the efficiency of the grinder and the distribution of mechanical stresses in the roller and the track, the track (14) and the roller (16) are designed in such a way that the gap between them decreases from the edge of the track (14) located on the side for supplying the material to be ground to a distance from this edge at least equal to 80% of the width of the track, and in that this interval then swiftly increases to form a decompression area (19) on the ground material evacuation side.

TECHNICAL FIELD

The present invention relates to grinders comprising an annular trackwith a horizontal axis, a roller capable of travelling over the saidtrack, means for pressing the roller against the track and means fordisplacing the material from one edge of the track to the other, in sucha way that it can pass several times beneath the roller before beingevacuated.

BACKGROUND ART

To enhance grinding when the materials to be ground are of heterogeneousgrain sizes, it is proposed (French patent No. 91.09788) to give theroller and/or the track a profile such that the gap between the rollerand the track decreases progressively or by degrees from one edge of thetrack to the other.

The object of the present invention is to enhance the efficiency of thegrinders of this type and to achieve a better distribution of themechanical stresses in the roller and the track.

SUMMARY OF THE INVENTION

The grinder to which the present invention relates is characterized inthat the gap between the roller and the track decreases from the edge ofthe track located on the side for feeding the material to be ground to adistance from the said edge at least equal to 80% of the width of thetrack, and then increases more quickly to form an area of decompressionon the ground material evacuation side.

According to a preferred form of embodiment, the track is constituted bya ring integral with a drum having a horizontal axis which forms asupply chamber on one side of the track and an evacuation chamber on theother side, and an annular barrier is provided at the end of theevacuation chamber opposite that adjoining the track to maintain in thesaid chamber a layer of ground material the thickness of which is suchthat it practically reaches the edge of the roller in the plane of theadjacent edge of the track.

Preferably, the axial extent of the decompression area counting from theedge of the track located on the material evacuation side, is between 2%and 20%, preferably 5% and 15%, of the width of the track, and, in thisarea, the angle formed by the track and the peripheral surface of theroller, in the plane containing the axes of the track and the roller, isless than 50°.

According to one form of embodiment of the grinder, the track iscylindrical and the roller is formed by at least two frustoconicalparts, a first part the diameter of which increases from its end locatedon the supply side to a distance from this end at least equal to 80% ofthe axial length of the roller, and a second part of decreasing diameterlocated at its other end.

Alternatively, the track can have a frustoconical profile with adiameter that decreases from its edge located on the side for supplyingthe material to be ground to the decompression area and a constant orvariable angle at the apex; in the decompression area, the diameter ofthe track increases in the direction of progress of the material. Withsuch a track, use can be made of a cylindrical roller the axis of whichwill be parallel with axis of the track or will form an angle of lessthan 5° therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The description that follows refers to the accompanying drawings whichshow, by way of non-limitative examples, several forms of embodiment ofthe invention, and in which:

FIG. 1 is a vertical section of a grinder produced according to theinvention;

FIG. 2 is a section, through a plane perpendicular to the axis of thegrinder of FIG. 1; and

FIGS. 3 and 4 illustrate two other forms of embodiment of the invention.

The grinder shown in the drawings is constituted by a drum 10, with ahorizontal axis, which is supported by shoes or skids 12 enabling it torotate about its axis ; these shoes could be replaced by a bushing orrollers. The drum is driven in rotation by conventional means, notshown, for example by a motor and a reducer the output shaft of whichbears a pinion engaged with a toothed wheel fixed to the drum.

The drum is constituted by a shell internally lined with wear plateswhich, in the central portion, form an annular grinding track 14, with acylindrical surface. The interior of the drum is thus divided into asupply area 11, a grinding area 13 and an evacuation area 15. Annularrims 17 provided at the two ends of the shell form barriers enabling alayer of material to be held in the supply and evacuation areas. Thisdrum is closed at its two ends by metal sheets mounted on a fixedsupport and to which are connected a supply chute, at one end, and adischarge chute and a suction conduit for the pneumatic evacuation ofthe fine particles, at the other end.

A roller 16 is mounted inside the drum, so as to be able to travel overthe track 14 when the drum is driven in rotation. More precisely, whenthe grinder is in operation, the roller travels over the layer ofmaterial covering the track. The roller is provided with two shaft endsmounted in bearings fixed to two levers disposed outside the drums, oneither side thereof. Springs or hydro-pneumatic jacks acting on thebearings or on the levers enable the roller to be pressed against thegrinding track with a predetermined, adjustable force.

Roller 16 is composed of three frustoconical portions, of differentconicity. The main two parts, 16a and 16b, extend over approximately 80%of the length of the roller; their diameter increases in the directionof progress of the material over the track (direction of the arrow inFIG. 1) and the angle at the apex of part 16a, the one closest to thesupply area, is greater that of part 16b. Part 16c, located on theevacuation area side, has a diameter that decreases in the direction ofprogress of the material and its angle at the apex is markedly greaterthan that of the other two parts, but less than 100°; the axial lengthof this part represents between 2% and 20%, preferably between 5% and15%, of the useful length of the roller. It delimits with the track adecompression area 19 which follows on from the zone for placing thematerial under pressure between the roller and the track. Thisdecompression area and the layer of material 20 formed in the evacuationarea oppose sudden ejection of the material compressed between the trackand the roller, close to the edge of the roller, (edge effect). Thismakes it easier to control crushing in the area adjacent to thedecompression area. Furthermore, the decompression area makes itpossible to ensure better distribution of the mechanical stresses in theroller close to its lateral face. The thickness of the layer of material20 formed in evacuation area 15 is such that it practically reaches theedge of the roller in the plane of the edge of the track adjacent tothis area.

A device designed to ensure the stepwise forward feeding of thematerial, from one end of the drum to the other, is disposed in theupper half of the latter, on the descending portion of the circulartrajectory of the materials. This device is schematically represented inFIG. 1 by a series of inclined strips 18 which detach from the wall ofthe drum and the track the material that is normally held there bycentrifugal force. The detached material slides over the strips 13 and,owing to their inclination, is moved there from the input towards theoutput of the grinder. By adjusting the inclination of strips 18, thespeed of forward feed of the material is regulated; different speeds canbe chosen for the feeding, grinding and evacuation areas. Alternatively,the device for the forward feeding of the material could be of the typedescribed in aforementioned French patent No. 91.09788.

In FIG. 3 is schematically represented another form of embodiment of thetrack and the roller. Instead of being cylindrical, the track is formedby three frustoconical surfaces, 14a, 14b and 14c adjoining in such away that its diameter decreases in the direction of progress of thematerial indicated by the arrow, over the greater part of its width, andthen swiftly decreases in its final portion. The angle at the apex ofsurface 14a is greater than that of surface 14b. Surface 14c of thetrack and the roller define the decompression area. In the plane of thefigure, which contains the axes of the roller and the track, the angle αformed by this portion of the track and the roller is less than 50°. Thesurface of roller 16 is cylindrical and its axis is parallel to that ofthe track.

In the form of embodiment shown in FIG. 4, the track comprises a firstfrustoconical portion, the diameter of which decreases in the directionof progress of the material (arrow), and a second cylindrical portion.The roller is cylindrical and its axis is inclined in relation to theaxis of the track by an angle β°of less than 5°. It comprises at its endadjacent to the evacuation area a frustoconical portion defining, withthe track, a decompression area.

Other forms of track and roller can be chosen to obtain a gap thatdecreases, in the direction of progress of the material, between thetrack and the roller, over the greater part of the width of the track,and to provide a decompression area on the evacuation area side; it goeswithout saying that all these forms are within the scope of theinvention. It is clear, moreover, that the invention also applies togrinders comprising several rollers on one and the same track or onseveral tracks.

We claim:
 1. Grinder, including at least one annular track with ahorizontal axis (14), at least one roller (16) capable of travellingover the said track, means for pressing the roller against the track,and means for displacing the material from one edge to the other of thetrack in such a way that it passes several times beneath the rollerbefore being discharged, with the gap between the roller (16) and thetrack (14) decreasing in the direction of advance of the material to becrushed, wherein the said gap between the roller (16) and the track (14)decreases from the edge of the track located on the side of supply ofthe material to be crushed to a distance from this edge at least equalto 80% of the width of the track, and in that this gap then rapidlyincreases to form a decompression area (19) on the crushed materialdischarge side, and in that the track (14) is constituted by a ringintegral with a coaxial drum (10) which forms a discharge chamber (15)on one side of the track, and an annular barrier (17) is provided at theend of the discharge chamber the furthest from the track to maintain, inthe said chamber, a layer of crushed material the thickness of which issuch that it practically reaches the edge of the roller in the plane ofthe adjacent edge of the track.
 2. Grinder according to claim 1,wherein; in the plane containing the axis of the roller and of thetrack, the angle (α) formed by the track and the roller in thedecompression area (19) is less than 50°.
 3. Grinder according to claim1 wherein the track (14) is cylindrical and the roller is formed by atleast two frustoconical parts, a first part (16a, 16b) the diameter ofwhich increases from its end located on the supply side to a distancefrom this end at least equal to 80% of the axial length of the roller,and a second part (16c) of decreasing diameter, located at its otherend.
 4. Grinder according to claim 1 wherein the track is formed by atleast two frustoconical surfaces, a first surface (14a, 14b) thediameter of which decreases from its edge located on the supply side toa distance from this edge at least equal to 80% of the width of thetrack, and a second surface (14c) of a decreasing diameter, adjacent toits other edge.
 5. Grinder according to claim 1 wherein the axis of theroller is inclined in relation to the axis of track by an angle (β) ofless than 5°.